This disclosure relates to a method for joining dissimilar metals and to articles comprising the same.
Dissimilar metals are often in contact with one another in a variety of different devices, such as, for example, automobiles, aircraft, building frames, and the like. Design engineers are therefore increasingly faced with the need to join dissimilar materials as they are seeking creative new structures or parts with tailor-engineered properties. Sometimes a part needs high-temperature resistance in one area, good corrosion resistance in another, and so on. Structures may need toughness or wear resistance in one area combined with high strength in another location. Improving the ability to join dissimilar materials with engineered properties are enabling new approaches to light-weighting automotive structures, improving methods for energy production, creating next generation medical products and consumer devices, and many other manufacturing and industrial uses.
Joining dissimilar materials is often more difficult than joining the same material or alloys with minor differences in composition; however, many dissimilar materials can be joined successfully with the appropriate joining process and specialized procedures.
While it may be advantageous to use dissimilar metals in such devices to take advantage of properties such as lower weight, increased stiffness or elasticity, better electrical conductivity, and the like, galvanic corrosion often results because one metal often corrodes preferentially with respect to the other when both metals are in electrical contact.
Dissimilar metals and alloys have different electrode potentials, and when two or more come into contact in the presence of an electrolyte, one metal acts as anode and the other as cathode. The electro-potential difference between the dissimilar metals is the driving force for an accelerated attack on the anode member of the galvanic couple.
In automobiles, the problem of galvanic corrosion is often mitigated by disposing an electrically insulating layer of polymer adhesive between the dissimilar metals. The presence of the electrically insulating layer prevents galvanic corrosion and enables a variety of different dissimilar metals to be bonded together. The use of the electrically insulating layer while mitigating the effects of corrosion however, gives rise to other problems. One problem wrought by the adhesive bonding of these different metals is that it involves using a wide variety of different weld schedules. This produces a problem with the speed and efficiency of manufacturing automobiles. Another problem brought on by the problem of an electrically insulating layer between two electrically conducting layers of metal involves the reception of radio-frequency signals in the automobile.
It is therefore desirable to devise methods for manufacturing articles that comprise dissimilar metals by joining the metals in a manner that reduces the tendency towards galvanic corrosion, reduces weld schedules and improves radio frequency reception in automobiles.